This invention concerns clutch or brake units and more particularly clutches or brakes which are electromagnetically operated.
In U.S. Pat. No. 4,079,821 there is disclosed an electromagnetically operated clutch of the type having an inner body and an armature member, the inner body having radially spaced pole faces separated by a nonmagnetic ring. The clutch includes an electromagnetic coil causing magnetic flux to pass from the inner body outer pole face, through the armature and back through the inner pole face to act to draw the inner body and armature into driving relationship to establish drive through the clutch unit.
The clutch unit disclosed in that patent features a torque booster arrangement comprising of a plurality of balls cooperating with corresponding pocket sets which serve to augment the engagement pressure by the camming action developed between the balls and the pockets upon engagement of the pole faces with the armature. The particular design of this torque boosting feature produces extremely rapid actuation of the clutch, considerably faster than other clutches of similar type.
While this may be advantageous in many applications, this rapid actuation may be required to modify in certain situations requiring a slower torque buildup. While this could be carried out electrically, this requires modification of the actuation circuitry which must then be changed from that for other conventional clutch designs which may not be a suitable alternative design option.
Accordingly, it is an object of the present invention to provide an electromagnetically operated clutch unit in which the torque buildup is delayed but which does not require a change in the external control circuit energizing the clutch unit.
It is another object of the present invention to achieve such objective in a simple, reliable manner which does not require complex additions or changes in configuration of the clutch unit.
It is yet another object of the present invention to provide such a delayed torque buildup which does not substantially affect the final torque output of the unit.